Head-Up-Display (HUD) systems enable drivers to view crucial information without the need to look away from the road. Hence HUD systems have become an increasingly important component for automotive use to enhance road safety.
Augmented Reality (AR), provides a three-dimensional (3D) viewing experience. A number of technologies have been developed to provide 3D AR, the most relevant of which are as follows:
U.S. Pat. No. 8,521,411 B2 (Grabowski, Aug. 27, 2013) describes a HUD system that allows a continuous depth volumetric image by rapid mechanical scanning of a lens to re-image a laser beam into floating space. “Opt. Express 14, 12760-12769 (2006)” discloses a method of showing volumetric 3D images with a rapidly rotating mirror scanner to produce multiple slices of inclined images. These mechanical systems suffer from mechanical wear over time and may easily suffer from shock damage if they are not mechanically isolated from the vehicle. Further, the former system would only provide a cable image and hence can only display very limited information to the driver.
US20040164927A1 (Suyama, Aug. 26, 2004) describes a system where a liquid crystal Fresnel lens with a rapidly variable focal length is used to re-image a display panel to produce a volumetric image. The lens used for this system requires a large variation in power and a fast switching speed. For the system to work, the lens would either need to be very thick, which would compromise its switching speed, or have very small Fresnel zone size, which would compromise its image quality. For the lens to switch fast enough to display large depth variation volumetric images, a special type of “dual-frequency” liquid crystals will be required. This type of liquid crystal has not yet been utilized in mass display products, may not necessarily meet automotive standards, and may be expensive to be used in large volume production.
JP2004168230A describes an automotive HUD system that uses multiple pixelated liquid crystal panels and an ordinary backlight unit to display images at different depths. Such a system will have a very low optical efficiency, meaning the system will consume significant power to achieve high brightness required by automotive displays. The system would also have a limited display contrast, which is a known limitation of liquid crystal display panels with ordinary backlights.
U.S. Pat. No. 5,764,317 (Sadovnik, Jun. 9, 1988) and U.S. Pat. No. 6,100,862 (Sullivan, Aug. 8, 2000) describe systems that produce volumetric images by using a projector to sequentially project a different image onto an array of switchable screens. However, these systems are only capable of displaying images at discrete depth planes. Since the screens can never be fully transparent, haze will become noticeable if the number of screens is increased in attempt to display a pseudo-continuous volumetric image.
U.S. Pat. No. 4,670,744 (Buzak, Jun. 2, 1987) describes a system that uses a stack of cholesteric liquid crystal as switchable mirrors to change the optical distance between a display panel and the observer. The switchable reflectors are highly dependent on wavelength and angle of the incident light, making it unsuitable for full-color displays.
Currently there is no augmented reality technology that can achieve low haze, can be manufactured at a relatively low cost, and provide continuous volume augmented reality that uses readily-mass-manufacturable materials that fit automotive performance and safety standards.